linux-kernel - Re: [PATCHv2] perf probe: Fix failure to add multiple probes without debuginfo

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Date:	Sat, 21 Mar 2015 21:19:21 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	He Kuang <hekuang@...wei.com>, a.p.zijlstra@...llo.nl,
	mingo@...hat.com, namhyung@...nel.org, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] perf probe: Fix failure to add multiple probes without
 debuginfo

(2015/03/20 22:50), Arnaldo Carvalho de Melo wrote:
> Em Fri, Mar 20, 2015 at 04:42:46PM +0900, Masami Hiramatsu escreveu:
>> (2015/03/20 10:56), He Kuang wrote:
>>> Perf tries to find probe function addresses from map when debuginfo
>>> could not be found.
>>>
>>> To the first added function, the value of ref_reloc_sym was set in
>>> maps__set_kallsyms_ref_reloc_sym() and can be obtained from
>>> host_machine->kmaps->maps. After that, new maps are added to
>>> host_machine->kmaps->maps in dso__load_kcore(), all these new added maps
>>> do not have a valid ref_reloc_sym.
>>>
>>> When adding a second function, get_target_map() may get a map without
>>> valid ref_reloc_sym, and raise the error "Relocated base symbol is not
>>> found".
>>>
>>> Fix this by using kernel_get_ref_reloc_sym() to get ref_reloc_sym.
>>>
>>> This problem can be reproduced as following:
>>>
>>>   $ perf probe --add='sys_write' --add='sys_open'
>>>   Relocated base symbol is not found!
>>>     Error: Failed to add events.
>>>
>>> After this patch:
>>>
>>>   $ perf probe --add='sys_write' --add='sys_open'
>>>   Added new event:
>>>     probe:sys_write      (on sys_write)
>>>
>>>   You can now use it in all perf tools, such as:
>>>
>>>       perf record -e probe:sys_write -aR sleep 1
>>>
>>>   Added new event:
>>>     probe:sys_open       (on sys_open)
>>>
>>>   You can now use it in all perf tools, such as:
>>>
>>>       perf record -e probe:sys_open -aR sleep 1
>>>
>>
>> OK, I've checked that this solve the problem :)
>>
>> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> 
> Ok, next time, please consider sending a Tested-by: tag instead, if what
> you did was to apply the patch, check that it fixes the problem, that
> provides a stronger patch endorsement.

I see. :)

Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

BTW, I've found another bug in perf probe for these sys_XXX functions.

----
# ./perf probe -vfn --add="sys_write" --add="sys_open"
probe-definition(0): sys_write
symbol:sys_write file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
probe-definition(1): sys_open
symbol:sys_open file:(null) line:0 offset:0 return:0 lazy:(null)
0 arguments
symsrc__init: cannot get elf header.
Looking at the vmlinux_path (7 entries long)
Using /usr/lib/debug/lib/modules/3.10.0-123.13.2.el7.x86_64/vmlinux for symbols
Open Debuginfo file: /usr/lib/debug/lib/modules/3.10.0-123.13.2.el7.x86_64/vmlinux
Try to find probe point from debuginfo.
Symbol sys_write address found : 3b0100
Failed to find debug information for address 3b0100
Probe point 'sys_write' not found.
  Error: Failed to add events. Reason: No such file or directory (Code: -2)
----

Something went wrong... :-( I'll check that.


Thank you,
> 
> - Arnaldo
>  
>>
>> Thank you!
>>
>>> Signed-off-by: He Kuang <hekuang@...wei.com>
>>> ---
>>>  tools/perf/util/probe-event.c | 4 +---
>>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>>> index c5e1338..c1ccd6a 100644
>>> --- a/tools/perf/util/probe-event.c
>>> +++ b/tools/perf/util/probe-event.c
>>> @@ -2507,7 +2507,6 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>>>  					    int max_tevs, const char *target)
>>>  {
>>>  	struct map *map = NULL;
>>> -	struct kmap *kmap = NULL;
>>>  	struct ref_reloc_sym *reloc_sym = NULL;
>>>  	struct symbol *sym;
>>>  	struct probe_trace_event *tev;
>>> @@ -2540,8 +2539,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
>>>  	}
>>>  
>>>  	if (!pev->uprobes && !pp->retprobe) {
>>> -		kmap = map__kmap(map);
>>> -		reloc_sym = kmap->ref_reloc_sym;
>>> +		reloc_sym = kernel_get_ref_reloc_sym();
>>>  		if (!reloc_sym) {
>>>  			pr_warning("Relocated base symbol is not found!\n");
>>>  			ret = -EINVAL;
>>>
>>
>>
>> -- 
>> Masami HIRAMATSU
>> Software Platform Research Dept. Linux Technology Research Center
>> Hitachi, Ltd., Yokohama Research Laboratory
>> E-mail: masami.hiramatsu.pt@...achi.com
>>
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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